This invention relates to a process for the preparation of 1-amino-naphthalene-7-sulphonic acid from 1-chloronaphthalene-4,7-disulphonic acid.
It is known that 1-amino-naphthalene-7-sulphonic acid can be prepared, for example, by sulphonating naphthalene, nitrating the resulting 2-naphthalenesulphonic acid and subsequently reducing this with iron (Beilstein H XIV, 765 and Ullmann, volume 12, 625 (1960)). 1-Amino-naphthalene-6-sulphonic acid is always formed as a by-product in this preparation and must be separated off.
The preparation of 1-amino-naphthalene-sulphonic acids by reacting the 1-chloro- and 1-bromo-naphthalene-sulphonic acids with ammonia at temperatures of 200.degree. to 210.degree. C is known (German Pat. No. 72,336). However, a disadvantage of this process is that the reaction proceeds very slowly when a catalyst is not used. According to German Pat. No. 72,336, if a reaction takes place, the corresponding 1-amino-monosulphonic, -disulphonic and -trisulphonic acids are respectively formed from 1-halogenonaphthalene monosulphonic, -disulphonic and -trisulphonic acids.